1. Technical Field of the Invention
The present invention relates to a printing system using a thermal printer and, more particularly, to a printing system using a thermal printer capable of printing background data such as to be visually clearly distinguished from also printed basic data.
2. Background of the Invention
The POS system permits various data such as sales data to be obtained in real time and is widely used in various shops such as convenience stores, supermarkets, restaurants and fast-food restraint in view point of sales tactics. The POS system is also used for printing ticket sheets for entrance tickets of concerts, attractions, etc., train tickets and airplane tickets.
In the POS system of this type, a bar code reader in each POS terminal reads out bar cods printed on sales items, thus taking out sales item data and item price data, or each register operator inputs item data and price data by terminal operation. The data taken out or inputted in this way, are fed out from the terminal to a processor as main unit for the execution of POS functions such as item management and sales amount management.
For recording details of sales data such as sales items and amounts, sales data are printed on each receipt by a printer provided with the terminal. Among the data printed on the receipt, are usually item name, unit price, total amount, consumption tax, gross total amount, deposited amount, change amount and date and are also shop data such as shop name. In the meantime, it has been largely desired and put to actual practice to additionally print particular data such as shop design marks and service messages on the receipts.
In the prior art printing on this type of receipts, the particular data are printed in fixed independent areas separate from item sales data on the receipt.
Japanese patent laid-open No. 9-226184 (FIG. 2, paragraphs [0015]–[00021]) (Patent reference 1) discloses a receipt printing system, in which when printing a shop name or like shop mark together with character data on the receipt, the shop mark image data which requires a long printing time is preliminarily read out. This system is an example of printing the shop mark in an independent place separate from item sales data.
In the meantime, printing of particular data as background data in superimposition on sales data as genuine basic data, is desired because of its capability of reduction of the paper quantity used and also reduction of the printing time. However, the printing of the two kinds of data in superimposition on each other, poses a problem that the visual recognition property of the genuine basic data is extremely deteriorated.
Also, the printer provided with the POS terminal used in the POS system should be inexpensive in price. For this reason, thermal printers are used. The prior art thermal printers, however, use a matrix array of color generation dots. Therefore, fine print density adjustment cannot be obtained, and print of basic data and background data and in superimposition on each other results in extreme deterioration of the visual recognition property of the two kinds of data.
FIG. 9 shows dot diagrams for explaining print examples based on an area gradation system using a prior art thermal printer. Referring to FIG. 9, data are printed by causing color generation of each of 8 by 8 dots as a unit. In the density expression printing by the prior art thermal printer, the density adjustment is performed by adjusting the number of color generation dots per unit area of the basis of this area gradation system. By way of example, FIG. 9(A) shows a high density expression case. In this case, all the dots are caused to generate color. FIG. 9(B) shows a low density expression case. In this case, substantially one half of the full dots are caused to generate color. FIG. 9(C) shows a medium density expression case. In this case, color generation of dots is caused in an adequate balance.
However, the density printing based on such area gradation is subject to a restriction that the print is very uncomforably viewed in case when a large number of gradations are provided for a small area.